For many years, the most usual vehicle or means of transportation for paraplegics and others has been the conventional wheelchair. The conventional wheelchair is a four wheel vehicle having two relatively large rear wheels and two smaller front wheels. The two front wheels are usually pivotally mounted so that the wheelchair can be turned or steered by independent rotation of the two large rear wheels. Typically, the two larger rear wheels are turned by manual manipulation, and for this purpose, an outer concentric rim is normally mounted on the wheel and the concentric rim is turned by the hand to drive and steer the wheelchair.
In recent years, there have been numerous developments which improve wheelchairs. These developments relate primarily to wheelchairs that are driven electrically by battery packs. The electrically driven wheelchairs serve their purpose and provide numerous advantages over the conventional manually manipulated wheelchairs but they also have many disadvantages or deficiencies such as the need to regularly recharge the batteries, the relatively high cost of the wheelchair, and the heavy weight of the motorized wheelchair.
There are numerous prior art devices that allow a person to propel and steer a wheelchair by means other than the manual manipulation of rims adjacent the relatively large rear wheels of the wheelchair. The following patents reflect the state of the art of which the applicant is aware insofar as they are germane or pertinent to his invention: U.S. Pat. No. 3,381,973 to Carr; U.S. Pat. No. 4,316,616 to Boivin; U.S. Pat. No. 4,471,972 to Young; U.S. Pat. No. 4,506,901 to Tosti; U.S. Pat. No. 5,312,127 to Oxford; and U.S. Pat. No. 5,501,480 to Ordelman et al.
The patent to Carr discloses a combination wheelchair and cot that includes a removable chair propelling attachment that can be either hand pedal or foot pedal operated, selectively, depending upon the preference or capabilities of the user. The patent to Boivin discloses a self-propelling and steering attachment for a wheelchair which can be installed and removed by the wheelchair user and which is power driven through a hand actuated crank mechanism through the intermediary of a multi-speed transmission whereby the user can select the right transmission ratio in accordance with the slope or type of ground on which he is travelling. The patent to Young discloses a propulsion and steering attachment for conventional wheelchairs which includes a frame, means for securing the frame to several types and sizes of conventional wheelchairs, steering and propelling means which include a hand crank and a single steerable front wheel, and means formed on the frame for allowing it to collapse for convenient storage. The patent to Tosti discloses a hand-propelled wheelchair which includes hand crank operated, chain and sprocket, direct drives to the rear, relatively large, wheels of the wheelchair to turn the rear wheels in either direction. The patent to Oxford discloses an attachment for a conventional wheelchair which allows the wheelchair occupant to propel and guide the wheelchair by reciprocating an actuating arm. The patent to Ordelman et al. discloses an attachment frame for a conventional wheelchair which includes a coupling assembly for attaching the frame to the wheelchair, at least one steerable wheel, and a hand crank for rotating the steerable wheel through chain and sprocket means for propelling the wheelchair.